The extreme nature of what rice -- is -- the byproduct. From the castor beans when castor oil is made. Highly deadly. It either can be inhaled ingested injected even the skin contact. Can be lethal form and often times. Death can occur would -- very short period of time sometimes within 36 hours if it is inhaled. Com there are some of the symptoms. It can be -- Johnson of severity. Nausea vomiting flu like symptoms respiratory problems. Seizures. And as we've seen before it has been used. Four threats to be made -- of people of high prominence politicians. And celebrities. And again the latest we've got right now -- that two. Letters have tested positive in these field tests for the presence of this -- -- but again as we do you want to make sure that we are cautioning that up further analysis must be done in a lab to determine if in fact. This rice and is present on these letters.

This transcript has been automatically generated and may not be 100% accurate.

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{"id":18979156,"title":"Ricin: What It Is and What It Can Do","duration":"1:04","description":"The poison, found naturally in castor beans, has been used experimentally to kill cancer cells.","url":"/Health/video/ricin-what-it-is-and-what-it-can-do-18979156","section":"Health","mediaType":"Default"}